It is usually required to determine the accuracy of coordinate positioning apparatus, for example coordinate measuring machines, and manual methods exist for doing so. For example, it is known to provide a test bar, operate the machine to measure the length of the bar in different locations of the bar in the coordinate field, and compare the possibly different results obtained at said different locations thereby to establish a measure of the accuracy of the apparatus. The bar itself has to be placed manually into the respective said positions, use being made of a frame or the line to support the bar in those positions. It is an object of this invention to provide a method of and device for checking coordinate positioning apparatus automatically or substantially automatically.